This should make it 100% clear that while you are bound by the license when you play around with the bundle itself and its contents, but what you create with the bundle is yours and not license-bound.
The other thing is the etiquette that prevails in the world of FOSS (Free and Open Source Software), where it is a question of good manners to give credit and name the means/tools used, so Krita and the Memileo Impasto Brushes.
This can also pay off for you, at least when you look at the big picture. If you promote both Krita and the brushes you used to create your artwork simply by naming them, you’ll entice people to try those tools.
Some of them will usually donate a certain amount to the project, which ultimately helps to keep Krita alive and improving. So in the long run, you will get better tools.
And giving credit doesn’t cost you anything.
Michelist